Processes for reduction of alkylation catalyst deactivation utilizing low silica to alumina ratio catalyst

ABSTRACT

Alkylation systems and methods of minimizing alkylation catalyst regeneration are described herein. The alkylation systems generally include a preliminary alkylation system adapted to receive an input stream including an alkyl aromatic hydrocarbon and contact the input stream with a preliminary alkylation catalyst disposed therein to form a first output stream. The preliminary alkylation catalyst generally includes a zeolite catalyst having a SiO 2 /Al 2 O 3  ratio of less than about 25. The alkylation systems further include a first alkylation system adapted to receive the first output stream and contact the first output stream with a first alkylation catalyst disposed therein and an alkylating agent to form a second output stream.

FIELD

Embodiments of the present invention generally relate to alkylation ofaromatic compounds. In particular, embodiments of the inventiongenerally relate to reducing the deactivation of the alkylation catalystwithin alkylation systems.

BACKGROUND

Alkylation reactions generally involve contacting a first aromaticcompound with an alkylation catalyst to form a second aromatic compound.Unfortunately, alkylation catalysts generally experience deactivationrequiring either regeneration or replacement. Some of the deactivationresults from poisons present in the input stream to the alkylationsystem. Therefore, a need exists to develop an alkylation system that iscapable of reducing alkylation catalyst deactivation.

SUMMARY

Embodiments of the present invention include alkylation systems. Thealkylation systems generally include a preliminary alkylation systemadapted to receive an input stream including an alkyl aromatichydrocarbon and contact the input stream with a preliminary alkylationcatalyst disposed therein to form a first output stream. The preliminaryalkylation catalyst generally includes a zeolite catalyst having aSiO₂/Al₂O₃ ratio of less than about 25. The alkylation systems mayfurther include a first alkylation system adapted to receive the firstoutput stream and contact the first output stream with a firstalkylation catalyst disposed therein and an alkylating agent to form asecond output stream.

In one embodiment, the alkylation system includes a preliminaryalkylation catalyst having a first SiO₂/Al₂O₃ ratio and a firstalkylation catalyst having a second SiO₂/Al₂O₃ ratio, wherein the firstSiO₂/Al₂O₃ ratio is lower than the second SiO₂/Al₂O₃ ratio.

Embodiments further include methods of minimizing alkylation catalystregeneration. Such methods generally include substantially continuouslyintroducing an alkyl aromatic hydrocarbon and an alkylating agent to analkylation system having an alkylation catalyst disposed therein,contacting the input stream with the alkylation catalyst to form anoutput stream and withdrawing the output stream from the alkylationsystem over a period of time substantially equal to a life of thealkylation catalyst. The methods further include contacting the inputstream with a preliminary catalyst including a zeolite catalyst having aSiO₂/Al₂O₃ ratio of 25 or less prior to feeding the input stream to thealkylation system. Such methods generally result in an alkylationcatalyst life that is longer than the same alkylation catalyst's life inthe absence of contact with the preliminary catalyst.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates an embodiment of an alkylation system.

FIG. 1B illustrates an embodiment of a separation system.

DETAILED DESCRIPTION Introduction and Definitions

A detailed description will now be provided. Each of the appended claimsdefines a separate invention, which for infringement purposes isrecognized as including equivalents to the various elements orlimitations specified in the claims. Depending on the context, allreferences below to the “invention” may in some cases refer to certainspecific embodiments only. In other cases it will be recognized thatreferences to the “invention” will refer to subject matter recited inone or more, but not necessarily all, of the claims. Each of theinventions will now be described in greater detail below, includingspecific embodiments, versions and examples, but the inventions are notlimited to these embodiments, versions or examples, which are includedto enable a person having ordinary skill in the art to make and use theinventions when the information in this patent is combined withavailable information and technology.

Various terms as used herein are shown below. To the extent a term usedin a claim is not defined below, it should be given the broadestdefinition persons in the pertinent art have given that term asreflected in printed publications and issued patents. Further, unlessotherwise specified, all compounds described herein may be substitutedor unsubstituted and the listing of compounds includes derivativesthereof.

The term “activity” refers to the weight of product produced per weightof the catalyst used in a process per hour of reaction at a standard setof conditions (e.g., grams product/gram catalyst/hr).

The term “alkylation” refers to the addition of an alkyl group toanother molecule.

The term “deactivated catalyst” refers to a catalyst that has lostenough catalyst activity to no longer be efficient in a specifiedprocess. Such efficiency is determined by individual process parameters.Further, the time from introduction of the catalyst to a system to thepoint that the catalyst is a deactivated catalyst is generally referredto as the catalyst life.

The term “processing” is not limiting and includes agitating, mixing,milling, blending and combinations thereof, all of which are usedinterchangeably herein. Unless otherwise specified, the processing mayoccur in one or more vessels, such vessels being known to one skilled inthe art.

The term “recycle” refers to returning an output of a system as input toeither that same system or another system within a process. The outputmay be recycled to the system in any manner known to one skilled in theart, for example, by combining the output with an input stream or bydirectly feeding the output into the system. In addition, multipleinput/recycle streams may be fed to a system in any manner known to oneskilled in the art.

The term “regeneration” refers to a process for renewing catalystactivity and/or making a catalyst reusable after its activity hasreached an unacceptable/inefficient level. Examples of such regenerationmay include passing steam over a catalyst bed or burning off carbonresidue, for example.

The term “molecular sieve” refers to a material having a fixed,open-network structure, usually crystalline, that may be used toseparate hydrocarbons or other mixtures by selective occlusion of one ormore of the constituents, or may be used as a catalyst in a catalyticconversion process. The term “zeolite” refers to a molecular sievecontaining a silicate lattice, usually in association with somealuminum, boron, gallium, iron, and/or titanium, for example. In thefollowing discussion and throughout this disclosure, the terms molecularsieve and zeolite will be used more or less interchangeably. One skilledin the art will recognize that the teachings relating to zeolites arealso applicable to the more general class of materials called molecularsieves.

FIG. 1 illustrates a schematic block diagram of an embodiment of analkylation/transalkylation process 100. Although not shown herein, theprocess stream flow may be modified based on unit optimization so longas the modification complies with the spirit of the invention, asdefined by the claims. For example, at least a portion of any overheadfraction may be recycled as input to any other system within the processand/or any process stream may be split into multiple process streaminputs, for example. Also, additional process equipment, such as heatexchangers, may be employed in the processes described herein and suchuse is generally known to one skilled in the art. Further, whiledescribed below in terms of primary components, the streams indicatedbelow may include any additional components as known to one skilled inthe art.

As shown in FIG. 1A, the process 100 generally includes supplying aninput stream 102 (e.g., a first input stream) to an alkylation system104 (e.g., a first alkylation system). The alkylation system 104 isgenerally adapted to contact the input stream 102 with an alkylationcatalyst to form an alkylation output stream 106 (e.g., a first outputstream). In addition to the input stream 102, an additional input, suchas an alkylating agent, may be supplied to the alkylation system 104 vialine 103.

At least a portion of the alkylation output stream 106 passes to aseparation system 107 (see, FIG. 1B). The separation system 107generally includes a plurality of vessels, such vessels being adapted toseparate components of the output stream 106. As shown in FIG. 1B, atleast a portion of the separation system output 120, described infurther detail below, is passed from the separation system 107 to asecond alkylation system 121 (e.g., a transalkylation system) astransalkylation input 120.

In addition to the transalkylation input 120, an additional input, suchas additional aromatic compound, may be supplied to the secondalkylation system 121, which may alternatively be referred to as atransalkylation system, via line 122 to contact a transalkyationcatalyst disposed therein and form a transalkylation output 124.

The input stream 102 generally includes a first aromatic compound. Thearomatic compound may include substituted or unsubstituted aromaticcompounds. If present, the substituents on the aromatic compounds may beindependently selected from alkyl, aryl, alkaryl, alkoxy, aryloxy,cycloalkyl, halide and/or other groups that do not interfere with thealkylation reaction, for example. Examples of substituted aromaticcompounds generally include toluene, xylene, isopropylbenzene, normalpropylbenzene, alpha-methylnaphthalene, ethylbenzene, mesitylene,durene, cymene, butylbenzene, pseudocumene, o-diethylbenzene,m-diethylbenzene, p-diethylbenzene, isoamylbenzene, isohexylbenzene,pentaethylbenzene, pentamethylbenzene, 1,2,3,4-tetraethylbenzene,1,2,3,5-tetramethylbenzene, 1,2,4-triethylbenzene,1,2,3-trimethylbenzene, m-butyltoluene, p-butyltoluene,3,5-diethyltoluene, o-ethyltoluene, p-ethyltoluene, m-propyltoluene,4-ethyl-m-xylene, dimethylnaphthalenes, ethylnaphthalene,2,3-dimethylanthracene, 9-ethylanthracene, 2-methylanthracene,o-methylanthracene, 9,10-dimethylphenanthrene and 3-methyl-phenanthrene.Further examples of aromatic compounds include hexylbenzene,nonylbenzene, dodecylbenzene, pentadecylbenzene, hexyltoluene,nonyltoluene, dodecyltoluene and pentadecytoluene.

In one embodiment, the aromatic compound includes one or morehydrocarbons, such as benzene, naphthalene, anthracene, naphthacene,perylene, coronene and phenanthrene, for example. In another embodiment,the first aromatic compound includes benzene. The benzene may besupplied from a variety of sources, such as a fresh benzene sourceand/or a variety of recycle sources, for example. As used herein, theterm “fresh benzene source” refers to a source including at least about95 wt. % benzene, at least about 98 wt. % benzene or at least about 99wt. % benzene, for example.

The alkylating agent may include olefins (e.g., ethylene, propylene,butene and pentene), alcohols (e.g., methanol, ethanol, propanol,butanol and pentanol), aldehydes (e.g., formaldehyde, acetaldehyde,propionaldehyde, butyraldehyde and n-valeraldehyde) and/or alkyl halides(e.g., methyl chloride, ethyl chloride, propyl chloride, butyl chlorideand pentyl chloride), for example. In one embodiment, the alkylatingagent includes a mixture of light olefins, such as mixtures of ethylene,propylene, butene and/or pentenes, for example. In another embodiment,the alkylating agent includes ethylene.

In addition to the first aromatic compound and the alkylating agent, theinput stream 102 and/or line 103 may further include other compounds inminor amounts (e.g., sometimes referred to as poisons or inactivecompounds), such as C₇ aliphatic compounds and/or nonaromatic compounds,for example. In one embodiment, the input stream 102 includes less thanabout 3% of such compounds or less than about 1%, for example (e.g.,about 100 ppb or less, or about 80 ppb or less or about 50 ppb or less).

The alkylation system 104 generally includes one or more reactionvessels. The reaction vessels may include continuous flow reactors(e.g., fixed-bed, slurry bed or fluidized bed), for example. In oneembodiment, the alkylation system 104 includes a plurality ofmulti-stage reaction vessels (not shown). For example, the plurality ofmulti-stage reaction vessels may include a plurality of operablyconnected catalyst beds, such beds containing an alkylation catalyst(not shown). The number of catalyst beds is generally determined byindividual process parameters, but may include from 2 to 20 catalystbeds or from 3 to 10 catalyst beds, for example.

Such reaction vessels may be liquid phase, vapor phase, supercriticalphase or mixed phase reactors operated at reactor temperatures andpressures sufficient to maintain the alkylation reaction in thecorresponding phase, i.e., the phase of the aromatic compound, forexample. Such temperatures and pressures are generally determined byindividual process parameters. In one embodiment, the plurality ofstages within a reaction vessel may be operated with the same ordifferent catalyst and at the same or different temperatures and spacevelocities. Such temperatures and pressures are generally determined byindividual process parameters. However, liquid phase reactions may occurat temperatures of from about 160° C. to about 270° C. and pressures offrom about 400 psig to about 700 psig, for example. Vapor phasereactions may occur at temperatures of from about 350° C. to about 500°C. and pressures of from about 200 psig to about 355 psig, for example.

The alkylation catalyst may include a molecular sieve catalyst. Suchmolecular sieve catalyst may include zeolite beta, zeolite Y, 25M-5,zeolite MCM-22, zeolite MCM-36, zeolite MCM-49 or zeolite MCM-56, forexample. In one embodiment, the catalyst is a zeolite beta having asilica to alumina molar ratio (expressed as SiO₂/Al₂O₃ ratio) of fromabout 5 to about 200 or from about 20 to about 100, for example. In oneembodiment, the zeolite beta may have a low sodium content, e.g., lessthan about 0.2 wt. % expressed as Na₂O, or less than about 0.02 wt. %,for example. The sodium content may be reduced by any method known toone skilled in the art, such as through ion exchange, for example. (See,U.S. Pat. No. 3,308,069 and U.S. Pat. No. 4,642,226 (formation ofzeolite beta), U.S. Pat. No. 4,185,040 (formation of zeolite Y), U.S.Pat. No. 4,992,606 (formation of MCM-22), U.S. Pat. No. 5,258,565(formation of MCM-36), WO 94/29245 (formation of MCM-49) and U.S. Pat.No. 5,453,554 (formation of MCM-56), which are incorporated by referenceherein.)

In one specific embodiment, the alkylation catalyst includes a rareearth modified catalyst, such as a cerium promoted zeolite catalyst. Inone embodiment, the cerium promoted zeolite catalyst is a ceriumpromoted zeolite beta catalyst. The cerium promoted zeolite beta (e.g.,cerium beta) catalyst may be formed from any zeolite catalyst known toone skilled in the art. For example, the cerium beta catalyst mayinclude zeolite beta modified by the inclusion of cerium. Any method ofmodifying the zeolite beta catalyst with cerium may be used. Forexample, in one embodiment, the zeolite beta may be formed by mildlyagitating a reaction mixture including an alkyl metal halide and anorganic templating agent (e.g., a material used to form the zeolitestructure) for a time sufficient to crystallize the reaction mixture andform the zeolite beta (e.g., from about 1 day to many months viahydrothermal digestion), for example. The alkyl metal halide may includesilica, alumina, sodium or another alkyl metal oxide, for example. Thehydrothermal digestion may occur at temperatures of from slightly belowthe boiling point of water at atmospheric pressure to about 170° C. atpressures equal to or greater than the vapor pressure of water at thetemperature involved, for example.

The cerium promoted zeolite beta may have a silica to alumina molarratio (expressed as SiO₂/Al₂O₃ ratio) of from about 10 to about 200 orabout 50 to 100, for example.

The alkylation catalyst may optionally be bound to, supported on orextruded with any support material. For example, the alkylation catalystmay be bound to a support to increase the catalyst strength andattrition resistance to degradation. The support material may includealumina, silica, aluminosilicate, titanium and/or clay, for example.

The alkylation output 106 generally includes a second aromatic compoundformed from the reaction of the first aromatic compound and thealkylating agent in the presence of the alkylation catalyst, forexample. In a specific embodiment, the second aromatic compound includesethylbenzene.

The transalkylation system 121 generally includes one or more reactionvessels having a transalkylation catalyst disposed therein. The reactionvessels may include any reaction vessel, combination of reaction vesselsand/or number of reaction vessels (either in parallel or in series)known to one skilled in the art. Such temperatures and pressures aregenerally determined by individual process parameters. However, liquidphase reactions may occur at temperatures of from about 65° C. to about290° C. (e.g., the critical temperature of the first aromatic compound)and pressures of from about 800 psig or less, for example. Vapor phasereactions may occur at temperatures of from about 350° C. to about 500°C. and pressures of from about 200 psi to about 500 psi, for example.

The transalkylation output 124 generally includes the second aromaticcompound, for example. As stated previously, any of the process streams,such as the transalkylation output 124, may be used for any suitablepurpose or recycled back as input to another portion of the system 100,such as the separation system 107, for example.

The transalkylation catalyst may include a molecular sieve catalyst andmay be the same catalyst or a different catalyst than the alkylationcatalyst, for example. Such molecular sieve catalyst may include zeolitebeta, zeolite Y, zeolite MCM-22, zeolite MCM-36, zeolite MCM-49 orzeolite MCM-56, for example.

In a specific embodiment, the first aromatic compound includes benzeneand the first alkylating agent includes ethylene. In one embodiment, themolar ratio of benzene to ethylene entering the alkylation system 104may be from about 1:1 to about 30:1, or from about 1:1 to about 20:1 orfrom about 5:1 to about 15:1 and the space velocity may be from about 2to about 10, for example.

In a specific embodiment, the separation system (or product recovery)107 includes three separation zones (illustrated in FIG. 1B) operated atconditions known to one skilled in the art. The first separation zone108 may include any process or combination of processes known to oneskilled in the art for the separation of aromatic compounds. Forexample, the first separation zone 108 may include one or moredistillation columns (not shown), either in series or in parallel. Thenumber of such columns may depend on the volume of the alkylation output106 passing therethrough, for example.

The overhead fraction 110 from the first column 108 generally includesthe first aromatic compound, such as benzene, for example. The bottomsfraction 112 from the first separation zone 108 generally includes thesecond aromatic compound, such as ethylbenzene, for example. The bottomsfraction 112 further includes additional components, which may undergofurther separation in the second separation zone 114 and thirdseparation zone 115, discussed further below.

The second separation zone 114 may include any process known to oneskilled in the art, for example, one or more distillation columns (notshown), either in series or in parallel. The overhead fraction 116 fromthe second separation zone 114 generally includes the second aromaticcompound, such as ethylbenzene, which may be recovered and used for anysuitable purpose, such as the production of styrene, for example. Thebottoms fraction 118 from the second separation zone 114 generallyincludes heavier aromatic compounds, such as polyethylbenzene, cumeneand/or butylbenzene, for example, which may undergo further separationin the third separation zone 115.

The third separation zone 115 generally includes any process known toone skilled in the art, for example, one or more distillation columns(not shown), either in series or in parallel. In a specific embodiment,the overhead fraction 120 from the third separation zone 115 may includediethylbenzene and liquid phase triethylbenzene, for example. Thebottoms fraction 119 (e.g., heavies) may be recovered from the thirdseparation zone 115 for further processing and recovery (not shown).

Unfortunately, alkylation and transalkylation catalysts generallyexperience deactivation upon exposure to reaction. The deactivationresults from a number of factors. One of those factors is that poisonspresent in the input stream 102, such as nitrogen, sulfur and/or oxygencontaining impurities, either naturally occurring or a result of a priorprocess, may reduce the activity of the alkylation catalyst.

Therefore, the alkylation/transalkylation system 100 further includes apreliminary alkylation system 200. The preliminary alkylation inputstream 202 may be passed through the preliminary alkylation system 200prior to entry into the alkylation system 104 to reduce the level ofpoisons in the input stream 102, for example. In one embodiment, thelevel of poisons is reduced by at least 10%, or at least 20% or at least30% or at least 40% or at least 50%, for example.

The preliminary alkylation system 200 may be maintained at ambient or upto alkylation conditions, for example. For example, the preliminaryalkylation system 200 may be operated under liquid phase and/or vaporphase conditions. For example, the preliminary alkylation system 200 maybe operated at a temperature of from about 20° C. to about 270° C. and apressure of from about 675 kPa to about 8300 kPa.

The preliminary alkylation system 200 generally includes a preliminaryalkylation catalyst disposed therein. The alkylation catalyst,transalkylation catalyst and/or the preliminary catalyst may be the sameor different. In general, such catalysts include molecular sievecatalysts, such as zeolite Y or zeolite beta catalysts, for example.

As a result of the level of poisons present in the preliminaryalkylation input 202, the preliminary catalyst in the preliminaryalkylation system 200 has typically deactivated rapidly, requiringfrequent regeneration and/or replacement. For example, the preliminarycatalyst may experience deactivation more rapidly than the alkylationcatalyst (e.g., from about twice as often to about 1.5 times as often).Previous systems have generally used the preliminary alkylation system200 as a sacrificial system, thereby reducing the amount of poisonscontacting the alkylation catalyst in the alkylation system 104.

However, embodiments of the invention utilize a catalyst having a lowerSiO₂/Al₂O₃ ratio than those preliminary alkylation catalysts previouslyused (and discussed herein). For example, the preliminary alkylationcatalyst may have a SiO₂/Al₂O₃ ratio that is about 50 or less, or thatis about 25 or less, or that is from about 5 to about 50 or from about7.5 to about 25, for example.

In one specific, non-limiting embodiment, the preliminary alkylationcatalyst has a SiO₂/Al₂O₃ ratio that is lower than the SiO₂/Al₂O₃ ratioof the alkylation catalyst. For example, the preliminary alkylationcatalyst may have a SiO₂/Al₂O₃ ratio that is at least about 25%, or atleast about 50%, or at least about 75% or at least about 90% lower thanthe SiO₂/Al₂O₃ ratio of the alkylation catalyst.

The preliminary alkylation catalyst may include any commerciallyavailable catalyst having the SiO₂/Al₂O₃ ratio discussed herein. Forexample, the preliminary alkylation catalyst may include Y-84 zeolite(i.e., SiO₂/Al₂O₃ ratio of 9.1), for example.

Further, while not described in detail herein, it is contemplated thatthe preliminary alkylation catalyst may include a plurality ofpreliminary alkylation catalysts so long as at least one of theplurality of preliminary alkylation catalysts include the lowerSiO₂/Al₂O₃ ratio preliminary alkylation catalyst described herein.

Unexpectedly, it has been found that the embodiments described hereinresult in significantly reduced, if not eliminated, deactivation of allcatalysts within the alkylation system.

However, when regeneration of any catalyst within the system is desired,the regeneration procedure may includes processing the deactivatedcatalyst at high temperatures, although the regeneration may include anyregeneration procedure known to one skilled in the art.

Once a reactor is taken off-line, the catalyst disposed therein may bepurged. Off-stream reactor purging may be performed by contacting thecatalyst in the off-line reactor with a purging stream, which mayinclude any suitable inert gas (e.g., nitrogen), for example. Theoff-stream reactor purging conditions are generally determined byindividual process parameters and are generally known to one skilled inthe art.

The catalyst may then undergo regeneration. The regeneration conditionsmay be any conditions that are effective for at least partiallyreactivating the catalyst and are generally known to one skilled in theart. For example, regeneration may include heating the catalyst to atemperature or a series of temperatures, such as a regenerationtemperature of from about 50° C. to about 400° C. above the purging orreaction temperature, for example.

In one specific non-limiting embodiment, the alkylation catalyst isheated to a first temperature (e.g., 700° F.) with a gas containingnitrogen and about 2% oxygen, for example, for a time sufficient toprovide an output stream having an oxygen content of about 0.5%. Thecatalyst may then be heated to a second temperature for a timesufficient to provide an output stream having an oxygen content of about2.0%. The second temperature may be about 50° F. greater than the firsttemperature, for example. The second temperature is generally about 950°F. or less, for example. The catalyst may further be held at the secondtemperature for a period of time, or at a third temperature that isgreater than the second temperature, for example.

Upon catalyst regeneration, the catalyst may then be reused foralkylation and transalkylation, for example.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof and the scope thereof isdetermined by the claims that follow.

1. An alkylation system comprising: a preliminary alkylation systemadapted to receive an input stream and contact the input stream with apreliminary alkylation catalyst comprising a zeolite catalyst comprisinga SiO₂/Al₂O₃ ratio of less than about 25 disposed therein to form afirst output stream, wherein the input stream comprises an alkylaromatic hydrocarbon; and a first alkylation system adapted to receivethe first output stream and contact the first output stream with a firstalkylation catalyst disposed therein and an alkylating agent to form asecond output stream.
 2. The system of claim 1, wherein the alkylaromatic hydrocarbon comprises benzene.
 3. The system of claim 2,wherein the alkylating agent comprises ethylene and the second outputstream comprises ethylbenzene.
 4. The system of claim 1, wherein thefirst output stream comprises about 100 ppb or less of catalyst poisons.5. The system of claim 1, wherein the first output stream comprisesabout 50 ppb or less of catalyst poisons.
 6. The system of claim 1,wherein the input stream comprises a first level of catalyst poisons,the first output stream comprises a second level of catalyst poisons andthe second level is lower than the first level.
 7. The system of claim6, wherein the second level is at least 20% lower than the first level.8. The system of claim 1, wherein the first alkylation catalystcomprises a cerium promoted zeolite beta catalyst.
 9. An alkylationsystem comprising: a preliminary alkylation system adapted to receive aninput stream comprising an alkyl aromatic hydrocarbon and contact theinput stream with a preliminary alkylation catalyst to form a firstoutput stream; and a first alkylation system adapted to receive thefirst output stream and contact the first output stream with a firstalkylation catalyst disposed therein and an alkylating agent to form asecond output stream, wherein the preliminary alkylation catalystcomprises a first SiO₂/Al₂O₃ ratio and the first alkylation comprises asecond SiO₂/Al₂O₃ ratio and wherein the first SiO₂/Al₂O₃ ratio is lowerthan the second SiO₂/Al₂O₃ ratio.
 10. The system of claim 9, wherein thealkyl aromatic hydrocarbon comprises benzene.
 11. The system of claim10, wherein the alkylating agent comprises ethylene and the secondoutput stream comprises ethylbenzene.
 12. The system of claim 9, whereinthe first output stream comprises about 100 ppb or less of catalystpoisons.
 13. The system of claim 9, wherein the first output streamcomprises about 50 ppb or less of catalyst poisons.
 14. The system ofclaim 9, wherein the first alkylation catalyst comprises a ceriumpromoted zeolite beta catalyst.
 15. The system of claim 9, wherein thefirst SiO₂/Al₂O₃ ratio is at least about 50% lower than the secondSiO₂/Al₂O₃ ratio.
 16. The system of claim 9, wherein the firstSiO₂/Al₂O₃ ratio is at least about 75% lower than the second SiO₂/Al₂O₃ratio.
 17. A method of minimizing alkylation catalyst regenerationcomprising: contacting an alkyl aromatic hydrocarbon with a preliminarycatalyst comprising a zeolite catalyst comprising a SiO₂/Al₂O₃ ratio of25 or less prior to feeding the alkyl aromatic hydrocarbon to analkylation system; substantially continuously introducing the alkylaromatic hydrocarbon and an alkylating agent to the alkylation systemcomprising an alkylation catalyst disposed therein; contacting the alkylaromatic hydrocarbon with the alkylation catalyst to form an outputstream; and withdrawing the output stream from the alkylation systemover a period of time substantially equal to a life of the alkylationcatalyst, wherein the life of the alkylation catalyst is longer than thelife in an absence of contact with the preliminary catalyst.
 18. Themethod of claim 17, wherein the life of the alkylation catalyst islonger than a life of the preliminary catalyst.